Yes the difference is very visual. You will need 30 mm mounts. I have almost all 30 mm scopes now,so needless to say i have a pile of 1 inch mounts laying around. What i have found is as soon as you get to the more high power scopes you run into 30 mm tubes. I can't say the light is that much better. I have one rifle with a 1 inch tube and when i shoot early in the morning i can see no difference in light gathering. I am no scope pro for sure but i think when you get to higher power scopes you objective gets bigger,so the need for a 30 mm scope tube. Im sure someone else with a lot more knowledge will chime in

One inch is about 25mm. It's not that the diameter is that much larger but the area (think garden hose). Area of a 25mm tube 506mm, area of 30mm tube is 706mm and transmits about twice as much light. It's also the size of the front glass, bigger glass has better light gathering power. Many tubes have flared front ends to support larger glass.

According to the individual at Leupold who responded to my email, the 30mm tube allows a greater range of adjustments. The light transmission is determined by the objective lens.

This.

Actually the light gathering is determined by the objective lens, but at the point where the internal adjustments kick in the "pencil of light" from that lens has been tightened down to about 1/8" (3mm or so) so adding diameter allows more movment of the internal tube which is how you adjust your crosshairs.

Think of it this way. Draw a 1/8" circle on paper then draw a bigger 30mm (1 3/16") circle round it. Now draw a 1" (25.4mm) circle inside of the 30mm one, but outside the 1/8" one & you'll see how much more movment is possible for a scope with a 30mm tube as opposed to a 1" tube.***

Light Transmition is governed by design of the glass, optical coating efficiency & so on.

*** yes I know, these are approximate, but it does give a visual clue to how optical performance works. the 1/8" beam of light thrown back onto the internal tube is way smaller than either of the other 2 measurements, but it can "wander about more" in a bigger circle..

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